Components of SAP Application Layer:

We are aware that the actual processing of the user request done in application layer.

Let us know some components that the system (application layer) consists of,

Dispatcher:

The Dispatcher acts as an interface between the application layer (system) and the presentation layer (SAPGUI). The requests of the user from the presentation layer enter the application via a dispatcher as I discussed earlier. After the request is processed, the response to the user will be back through the dispatcher.

Dispatcher Queue:

Various work process types are stored in this queue. Before forwarding to work processes, request is stored in request queues first. Dispatcher follows First in First out rule (FIFO). It will find free work process and if available, it would be assign.

Buffer:

The Buffering (or a buffer) is the temporary storage area for data in order to perform transactions with those data. Usually, data are stored as Tables in underlying database. Transactions will be processing in an area called Work Process (WP) ( which means database fetching be done by WP). Frequently changing tables, (data) are stored in the buffer and transactions are processing with data from the buffer. It does not directly process with data from the underlying DB.

Gateway:

The Gateway is another type of an interface. This interface connects the application in the application layer with the underlying database layer. It enables communication between SAP system and between SAP system and external systems (ex: database layer/system).

Work Process (WP):

The Work Process is the actual transaction processing area in an application where it executes individual steps to be execute. Work Processes execute the dialog steps of application programs, i.e., it actually processes the transactions. (Please look into here for list of work processes).

Message:

Message is for Internal Communication between applications in the application layer. In addition, it handles communication between distributed Dispatchers in ABAP ( Advanced Business Application Programming) system (actual distribution of user’s request will be taken care here).